Touch sensing using shadow and reflective modes

ABSTRACT

A touch panel is described which uses at least one infrared source and an array of infrared sensors to detect objects which are in contact with, or close to, the touchable surface of the panel. The panel may be operated in both reflective and shadow modes, in arbirary per-pixel combinations which change over time. For example, if the level of ambient infrared is detected and if that level exceeds a threshold, shadow mode is used for detection of touch events over some or all of the display. If the threshold is not exceeded, reflective mode is used to detect touch events. The touch panel includes an infrared source and an array of infrared sensors.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation in part of U.S. utility applicationSer. No. 11/604,491 entitled “Infrared sensor integrated in a touchpanel” filed on Nov. 27, 2006, which is incorporated herein byreference.

BACKGROUND

Touch screens (or touch panels) are increasingly being used to provideuser interfaces for devices such as tablet PCs, self-service terminalsand mobile devices such as PDAs and mobile telephones. There are anumber of different technologies which may be used, for example aresistive touch panel in which touching the screen causes layers, whichare normally separated by a small gap, to come into contact or acapacitive touch panel in which contact with a conductive object changesthe capacitance.

In another example, a touch screen may use optical sensors (e.g. anoptical sensor array) to detect when a screen is touched. Use of opticalsensors enables multi-touch sensing, i.e. detection of multiplesimultaneous touches on the same screen. Such optical touch screens useone of two modes of operation: shadow mode or reflective mode. In shadowmode, the sensor detects the shadow which is cast by the object cominginto contact with the screen. This mode of operation is affected by thelevel of ambient visible lighting and if it is too dark there may be noshadow and so the touch screen will fail to detect touch events. Inreflective mode, the touch screen includes a light source (orilluminant) which illuminates objects which are brought into contactwith the screen. The sensor detects the light reflected back by theobjects. Where the touch screen includes an LCD screen, such that imagescan also be displayed on the screen, the image may affect the detectionof objects because different color regions will allow different amountsof light to be transmitted through. This therefore affects how much ofthe illuminant reaches the object and also how much of the reflectedlight reaches the sensor.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding to the reader. This summary is not anextensive overview of the disclosure and it does not identifykey/critical elements of the invention or delineate the scope of theinvention. Its sole purpose is to present some concepts disclosed hereinin a simplified form as a prelude to the more detailed description thatis presented later.

A touch panel is described which uses at least one infrared source andan array of infrared sensors to detect objects which are in contactwith, or close to, the touchable surface of the panel. The panel may beoperated in both reflective and shadow modes, in arbitrary per-pixelcombinations which change over time. For example, if the level ofambient infrared is detected and if that level exceeds a threshold,shadow mode is used for detection of touch events over some or all ofthe display. If the threshold is not exceeded, reflective mode is usedto detect touch events. The touch panel includes an infrared source andan array of infrared sensors.

Many of the attendant features will be more readily appreciated as thesame becomes better understood by reference to the following detaileddescription considered in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The present description will be better understood from the followingdetailed description read in light of the accompanying drawings,wherein:

FIG. 1 illustrates an exemplary interactive display system incorporatinga touch panel system;

FIG. 2 illustrates a cross-section through an exemplary touch panelsystem;

FIG. 3 illustrates a cross-section of an exemplary touch panel systemhaving an exemplary liquid crystal display incorporated therein;

FIG. 4 illustrates an exemplary active matrix circuit having a TFT-basedinfrared sensor integrated therein;

FIG. 5 shows a schematic diagram of a further touch panel which includesa mask layer behind an LCD panel;

FIG. 6 shows a schematic diagram of another exemplary touch panel;

FIG. 7 shows an example flow diagram of a method of reducing the powerconsumption of a touch panel;

FIG. 8 shows an example flow diagram of a method of distinguishingbetween objects in proximity to the touch panel;

FIG. 9 shows an example flow diagram of a method of operating a touchpanel system;

FIG. 10 shows another example flow diagram of a method of operating atouch panel system;

FIG. 11 shows a further example flow diagram of a method of operating atouch panel system;

FIG. 12 shows two example detected shapes, in reflective and shadowmodes of operation;

FIG. 13 is a schematic diagram of a first example of a touch panelsystem capable of communication with a nearby device;

FIG. 14 is an exemplary flow diagram of a method of operation of thesystem of FIG. 13;

FIG. 15 is a second exemplary flow diagram of a method of operation ofthe system of FIG. 13;

FIG. 16 is a schematic diagram of a second example of a touch panelsystem capable of communication with a nearby device; and

FIG. 17 illustrates an exemplary computing-based device in whichembodiments of the methods described herein may be implemented.

Like reference numerals are used to designate like parts in theaccompanying drawings.

DETAILED DESCRIPTION

The detailed description provided below in connection with the appendeddrawings is intended as a description of the present examples and is notintended to represent the only forms in which the present example may beconstructed or utilized. The description sets forth the functions of theexample and the sequence of steps for constructing and operating theexample. However, the same or equivalent functions and sequences may beaccomplished by different examples.

Use of infra-red sources as opposed to visible light, as described inU.S. utility application Ser. No. 11/604,491 entitled “Infrared sensorintegrated in a touch panel” filed on Nov. 27, 2006, which isincorporated herein by reference, has the benefit that the graphic imagedisplayed on the touch screen is not affected by the detection of touchevents. Additionally, the amount of ambient visible light does notaffect the detection.

FIG. 1 illustrates an exemplary interactive display system incorporatinga touch panel system. An interactive display system 100 comprises atouch panel system 102 coupled to a computer 104. Computer 104 may becontrolled via a monitor 106 and a keyboard 108 or any other suitableuser interface. Touch panel system 102 is thin and is generally placedon a flat surface, such as the top of a table 110 or hanging from awall. Touch panel system 102 comprises a touch panel and has a touchablesurface 112. The touch panel is, in this example, also a display, and agraphic image 114 displayed by the display is viewable via touchablesurface 112. In the example shown in FIG. 1, the graphic image 114 isthat of a maze. Computer 104 provides processing power that yields arich user interactive experience. As players move physical game pieces116 around the maze, touch panel system 102 is able to detect thelocation of the game pieces, and to alter the displayed graphic imageaccordingly. For example, the walls of the maze may be moved to increasethe complexity of the game, or a video clip may be shown if a game pieceis placed on a certain location in the maze.

Infrared (IR) sources in system 102 illuminate the physical game pieces116. IR radiation reflected from game pieces 116 is detected by IRsensors that are integrated into the touch panel. Signals from the IRsensors are processed by computer 104 to identify the locations ofphysical game pieces 116 on touchable surface 112. Any suitable methodfor distinguishing between different game pieces 116 on touchablesurface 112 may be used. For example, physical game pieces 116 may havedistinct shapes or may have symbols such as bar codes imprinted on theirundersides.

For example the touch panel comprises a plurality of retro-reflectiveopto sensors which operate in the infrared part of the spectrum. Eachsuch opto sensor comprises two components: an IR emitter and anoptically isolated IR light sensor. It is therefore capable of bothemitting light, and, at the same time, detecting the intensity ofincident light. If a reflective object is placed in front of the sensingelement, some of the emitted light will be reflected back and willtherefore be detected.

FIG. 2 illustrates a cross-section of an exemplary touch panel system. Atouch panel system 200 comprises a touch panel 202 that has severalinfrared (IR) sensors 204 integrated therein. Objects above a touchablesurface 206 include an object 208A that is in contact with touchablesurface 206 and an object 208B that is close to but not in actualcontact with (“adjacent”) touchable surface 206. Infrared sensors 204are distributed throughout touch panel 202 parallel to touchable surface206. One of infrared sensors 204 may detect infrared radiation reflectedfrom objects 208A and 208B, as indicated by arrows 210. Although theterm “above” is used in this description, it should be understood thatthe orientation of the touch panel system is irrelevant. As shown inFIG. 2, touchable surface 206 is horizontal, but in a differentembodiment generated by rotating system 200 clockwise by 90 degrees,touchable surface 206 could be vertical. In that embodiment, the objectsfrom which reflected IR radiation is detected are to the side oftouchable surface 206. The term “above” is intended to be applicable toall such orientations.

Touch panel 202 may comprise filters 212 that absorbs visible light andtransmits infrared radiation and are located between touchable surface206 and IR sensors 204 in order to shield IR sensors 204 from visiblelight 214 incident on touchable surface 206 in the case where IR sensors204 are sensitive to a broader range of wavelengths of light other thanpurely infrared wavelengths.

Touch panel 202 may comprise a display that is configured to displayimages that are viewable via touchable surface 206. An eye 215 indicatesa possible direction from which the images are viewed. The display maybe, for example, an LCD, an organic light emitting diode (OLED) display,a flexible display such as electronic paper, or any other suitabledisplay in which an IR sensor can be integrated.

System 200 may comprise a backlight 216 for the display. Backlight 216may comprise at least one IR source 218 that is configured to illuminateobjects in contact with or adjacent touchable surface 206 with infraredradiation through touchable surface 206, as indicated by arrows 220. IRsensor 204 s are only sensitive to radiation incident from above, so IRradiation traveling directly from backlight 216 to IR sensor 204 s isnot detected.

The output of IR sensors 204 may be processed to identify a detectedinfrared image. The IR radiation reflected from the objects may bereflected from reflective ink patterns on the objects, metal designs onthe objects or any other suitable reflector. For example, white paperreflects IR radiation and black ink absorbs IR radiation, so aconventional bar code on a surface of an object may be detected by aninfrared-sensing device according to the described technology. Fingersare estimated to reflect about 10% of the near IR, which is sufficientto detect that a finger or hand is located at a particular location onor adjacent the touchable surface. A higher resolution of IR sensors maybe used to scan objects to do applications such as document scanning andfingerprint recognition. For example, fingerprint recognition generallyrequires a resolution of more than 200 dots per inch (dpi).

FIG. 2 provides just one example of an exemplary touch panel system. Inother examples, the backlight may not comprise any IR sources and thetouch panel may include a frontlight which comprises at least one IRsource. In such an example, the touchable surface of the system is asurface of the frontlight and not of the touch panel. The frontlight maycomprise a light guide, so that IR radiation emitted from IR sourcetravels through the light guide and is directed towards touchablesurface and any objects in contact with or adjacent to it. In othertouch panel systems, both the backlight and frontlight may comprise IRsources. In yet other touch panel systems, there is no backlight and thefrontlight comprises both IR sources and visible light sources. Infurther examples, the system may not comprise a frontlight or abacklight, but instead the IR sources may be integrated within the touchpanel. In an implementation, the touch panel may comprise an OLEDdisplay which comprises IR OLED emitters and IR-sensitive organicphotosensors (which may comprise reverse-biased OLEDs).

In some touch panel systems, the touch panel may not comprise a display.Even if the touch panel comprises one or more components or elements ofa display, the touch panel may be configured as to not display anyimages. For example, this may be the case when the input tablet isseparate from the display. Other examples include a touchpad, a gesturepad, and similar non-display devices and components.

For some applications, it may be desirable to detect an object only ifit is in actual contact with the touchable surface of the touch panelsystem. The IR source of the touch panel system may be turned on only ifthe touchable surface is touched. Alternatively, the IR source may beturned on regardless of whether the touchable surface is touched, anddetection of whether actual contact between the touchable surface andthe object occurred is processed along with the output of the IR sensor.Actual contact between the touchable surface and the object may bedetected by any suitable means, including, for example, by a vibrationsensor or microphone coupled to the touch panel. A non-exhaustive listof examples for sensors to detect contact includes pressure-basedmechanisms, micro-machined accelerometers, piezoelectric devices,capacitive sensors, resistive sensors, inductive sensors, laservibrometers, and LED vibrometers.

IR sensors 204 may comprise suitable infrared-sensitive semiconductorelements. A non-exhaustive list of examples of semiconductor materialthat is infrared-sensitive includes polycrystalline silicon,monocrystalline silicon, microcrystalline silicon, nanocrystallinesilicon, plastic semiconductors and other non-silicon basedsemiconductors. Devices based on polycrystalline, microcrystalline,monocrystalline or nanocrystalline silicon may have better stabilitythan amorphous silicon devices. TFTs based on polycrystalline,microcrystalline, monocrystalline or nanocrystalline silicon may havehigher field mobility than amorphous silicon TFTs.

FIG. 3 illustrates a cross-section of an exemplary touch panel systemhaving an exemplary LCD incorporated therein. A touch panel system 300comprises a liquid crystal display 302 and a backlight 304. Backlight304 comprises arrays of light-emitting diodes (LEDs). In a colorbacklight, red LEDs 306, green LEDs 308 and blue LEDs 310 may be used.Liquid crystal display 302 typically comprises a diffuser 312 todisperse the light from backlight 304 and obtain a more uniformintensity over the surface of the display.

LCD 302 comprises a pair of polarizers 314 and 316 separated by a pairof glass substrates 318 and 320, which in turn are separated by a layerof liquid crystal material 322 contained in a cell gap betweensubstrates 318 and 320. In other implementations, substrates 318 and 320may be constructed from another transparent material, for example,plastic. Color filters, for example, a blue color filter (CF) 324 and ared color filter 326, are adjacent the inner surface of substrate 320.Each color filter transmits only part of the visible spectrum.

In the example shown in FIG. 3, LCD 102 is an active matrix LCD. Acontinuous electrode 328, termed “common electrode”, is located betweenthe color filters and liquid crystal material 322. Electrode 328 isconstructed using any suitable transparent electrode material, forexample, indium tin oxide (ITO). Individual pixel electrodes 330 may bepatterned from any suitable transparent electrode material, for example,ITO, and located on the inner surface of substrate 318. In a TFT activematrix LCD, substrate 318 includes TFTs which act as individual switchesfor each pixel electrode 330 (or group of pixel electrodes)corresponding to a pixel (or a group of pixels). The TFTs are describedin further detail below with respect to FIG. 6. Pixel electrodes 330,the TFTs, and substrate 318 form a backplane 332 of LCD 302.

It is known, although not widely, that polarizers and color filters losetheir function in the near infrared (IR) region of the spectrum. A sheetpolarizer no longer polarizes electromagnetic waves at wavelengthslarger than about 800 to 850 nm. Red, green and blue pigment colorfilters, typically used in LCDs, also transmit most of the wavelengthsin the near infrared region of the spectrum. Hence, some near infraredlight is transmitted through a conventional LCD, independent of theimage displayed on the LCD display screen. For example, 40% of the nearinfrared light incident on one surface (front or back) of a conventionalLCD may be transmitted through the LCD. The precise percentage of nearinfrared light transmitted through a particular LCD may depend onseveral factors, including, for example, the pixel aperture ratio andinternal reflections in the cell.

LCD 302 comprises an IR sensor 334 integrated therein. As shown in FIG.3, IR sensor 334 is integrated into backplane 332. Any IR lightreflected from an object 336 in contact with or adjacent a touchablesurface 337 of LCD 302 will be transmitted through polarizer 316,substrate 320, common electrode 328, liquid crystal material 322 anddetected by IR sensor 334. An arrow 338 indicates the IR light reflectedfrom object 336 and an arrow 340 indicates the IR light in liquidcrystal material 322, the IR light possibly attenuated by polarizer 316,substrate 320, and common electrode 328.

IR sensor 334 may include, for example, a polycrystalline silicon TFT orphotodiodes, a monocrystalline silicon TFT or photodiode, amicrocrystalline silicon TFT or photodiode, or a nanocrystalline siliconTFT or photodiode. Infrared-sensitive semiconductor materials that arenot based in silicon are also contemplated for elements of IR sensor334.

In order to block visible light from reaching IR sensor 334, anIR-transmitting and visible-light absorbing filter may be integrated inLCD 302 opposite IR sensor 334. If such a filter is integrated in LCD302, the susceptibility of the IR sensor to noise from ambient lighting342, may be reduced. In the example shown in FIG. 3, the filter is anIR-transmitting polymer black matrix 344. In other examples, the filtermay be comprised of two complementary color filters that areoverlapping, for example, blue color filter 324 and red color filter326. This implementation relies on the typical characteristics ofvisible light filters used in LCDs.

Backlight 304 comprises an IR source, which in this example is an IR LED346. IR LEDs are commercially available at a low cost at a range ofwavelengths, including, for example, peak emission wavelengths around900 nm: 850 nm, 860 nm, 870 nm, 880 nm, 890 nm, 935 nm, 940 nm and 950nm. At some of these wavelengths, high power versions of the IR LEDs areavailable. Infrared radiation from the IR source, indicated by an arrow348, is transmitted through LCD 302 after being diffused by diffuser312, if present. Some of the infrared radiation transmitted through LCD304 is reflected off object 336 and detected by IR sensor 334 asdescribed above.

As with FIG. 2, FIG. 3 provides just one example of an exemplary touchpanel system having an exemplary liquid crystal display incorporatedtherein. In other examples, the backlight may not comprise an IR sourceand instead a frontlight external to an outer surface of polarizer 316may be used. The frontlight may comprises an infrared light guide and anIR source coupled to light guide to direct the light away from the LCDtowards the objects which are in proximity or contact with the touchsurface. In another example, an IR source which emits polarized IRradiation may be used without a light guide and polarization filtersand/or reflectors blocking that polarization may be provided between thefrontlight and the LCD. IR light reflected off an object is notpolarized, will pass through the polarization filters and/or reflectors,and be detected by an IR sensor. In other embodiments, the touch panelsystem could comprise an LCD with an active matrix frontplane, a passivematrix backplane or a passive matrix frontplane. Whilst the example ofFIG. 3 shows an LCD with an IR-transmitting and visible-light absorbingfilter between the touchable surface of the system and the IR sensor, inother embodiments, the LCD may lack such a filter.

FIG. 4 illustrates an active matrix circuit having a TFT-based infraredsensor integrated therein. As is known in the art, an active matrixlayer comprises a set of data lines 400 and a set of select lines 402.An array of conductive lines may be created by including one data linefor each column of pixels across the display and one select line foreach row of pixels down the display. For each pixel, the active matrixlayer also comprises a pixel TFT 404 capacitively coupled to a commonline 406 through a capacitor 408. The source of pixel TFT 404 is coupledto its respective data line 400 and the drain of pixel TFT 404 iscoupled to its respective select line 402. To load the data to therespective pixels indicating which pixels should be illuminated,normally in a row-by-row manner, a set of voltages are imposed on therespective data lines 400 which imposes a voltage on the sources ofpixel TFTs 404. The selection of a respective select line 402,interconnected to the gates of pixels TFTs 404, permits the voltageimposed on the sources to be passed to drains of the pixel TFTs 404. Thedrains of the pixel TFTs are electrically connected to respective pixelelectrodes. In addition, a respective capacitance exists between thepixel electrodes enclosing the liquid crystal material, noted ascapacitances 409. Common line 406 provides a voltage reference. In otherwords, the voltage data (representative of the image to be displayed) isloaded into the data lines for a row of pixel TFTs 404 and imposing avoltage on select line 402 latches that data into the holding capacitorsand hence the pixel electrodes.

To integrate an IR sensor into the liquid crystal circuit, the activematrix layer also comprises an infrared-sensitive TFT 410 interconnectedto a readout TFT 412. The gate of readout TFT 412 may be interconnectedto select line 402, and the drain and the gate of infrared-sensitive TFT410 may be interconnected to a photobias line 414. (In otherimplementations, photobias line 414 and common line 606 may be one andthe same.) The source of readout TFT 412 may be interconnected to areadout line 416. A capacitor 417 may interconnect photobias line 414 tothe transistors. Readout line 416 is coupled to an operational amplifier418 connected to a reference voltage. The TFTs may be addressed by a setof multiplexed electrodes running along the gaps between the pixelelectrodes. Alternatively, the pixel electrodes may be on a differentlayer from the TFTs.

When a voltage is imposed on select line 402, this causes the voltage onreadout line 416 to be coupled to the drain of infrared-sensitive TFT410 and the drain of readout TFT 412, which results in a voltagepotential across capacitor 417. The state of infrared-sensitive TFT 410(“on” or “off”) will depend on whether IR radiation is incident oninfrared-sensitive TFT 410. For example, when a person touches thepanel, the IR reflection off the finger (about 10%) will turn theinfrared-sensitive TFT 410 partially “on”. If infrared-sensitive TFT 410is “off”, the voltage imposed across capacitor 417 will notsignificantly discharge through infrared-sensitive TFT 410, andaccordingly, the charge stored in capacitor 417 will be substantiallyunchanged. If infrared-sensitive TFT 410 is “on”, the voltage imposedacross capacitor 417 will significantly discharge throughinfrared-sensitive TFT 410, and accordingly, the charge stored incapacitor 417 will be substantially changed. To determine how muchcharge has leaked from capacitor 417, a voltage is imposed on selectline 402. This turns on readout TFT 412 and a charge flows throughreadout line 416 to reset the charge on capacitor 417. The outputvoltage of operational amplifier 418 is proportional or otherwiseassociated with the charge needed to reset the voltage on capacitor 417and is therefore a measure of the amount of IR radiation incident oninfrared-sensitive TFT 410 during the preceding frame time. This outputmay be processed along with the output from other IR sensors in thecircuit to identify a detected infrared image.

Infrared-sensitive TFT 410 and readout TFT 412, and the rest of thetransistors in the active matrix layer, may comprise any suitablesemiconductor material that is sensitive to infrared radiation,including polycrystalline silicon, monocrystalline silicon,microcrystalline silicon, nanocrystalline silicon, a plasticsemiconductor material, and semiconductor materials that are notsilicon-based.

For example, a microcrystalline silicon phototransistor can bemanufactured with Plasma chemical vapor deposition (CVD) equipment onthe same line as amorphous silicon TFTs. A large installed capacity isavailable for manufacturing a-Si TFT LCDs.

In another example the active matrix circuit may have a photodiode-basedinfrared sensor integrated therein. Such a circuit would differ fromthat of FIG. 4 in that an infrared-sensitive photodiode replaces theinfrared-sensitive TFT 410. The photodiode would be interconnected toreadout TFT 412, with the anode of photodiode interconnected tophotobias line 414, and the cathode of photodiode interconnected to thedrain of readout TFT 412. For example, the IR-sensitive photodiode maybe a lateral PIN diode of polycrystalline silicon, and can bemanufactured with a standard Low Temperature Poly Silicon ComplementaryMetal-Oxide Semiconductor (CMOS) process, which is common in the activematrix LCD industry.

A further exemplary active matrix circuit may have a TFT-based infraredsensor integrated therein. Such a circuit may comprise pixel circuitshaving two TFTs per pixel: a drive TFT and an access TFT. Each pixelcircuit also comprises a storage capacitor and an OLED coupled to acommon OLED electrode. The source of each access TFT is coupled to itsrespective data line and the drain of each access TFT is coupled to itsrespective select line. The access TFT is capacitively coupled to acommon bias line through storage capacitor. There are many othervariations of pixel circuits having two or more TFTs per pixel.

To integrate an IR sensor into the active matrix OLED circuit, theactive matrix layer also comprises an infrared-sensitive TFTinterconnected to a readout TFT in a similar manner to that shown inFIG. 4 and described above.

In another exemplary active matrix OLED circuit, an infrared-sensitivephotodiode may replace the infrared-sensitive TFT.

The IR sensors in a touch panel system according to the describedtechnology will also be sensitive to IR in the ambient radiation. Roomlight from incandescent lamps has a significant IR component. Likewise,in outdoor conditions, the solar spectrum at different times of the dayincludes IR radiation. It is known that the solar spectrum has a dip atabout 920 nm. Therefore, IR sources emitting a peak wavelength at ornear 920 nm may be used.

To improve signal-to-noise ratio in a touch panel system according tothe described technology, the IR source may be pulsed in synchronizationwith the detection by the IR sensor. For example, for a sensor thatintegrates the signal during the frame time, the IR source(s) may be“on” during the odd frames and “off” during the even frames. Thisrequires vertical scanning of the array of IR LEDs in the addressingdirection of the rows. The differential signal between odd frames andeven frames may cancel out the direct current (DC) noise from an IRbackground. The signal-to-noise ratio may also be improved by increasingthe intensity of the IR source.

In a further example, the illuminant (ie. the IR sources) may be cycledon and off at a particular frequency (e.g. 10 kHz) and the receivedsignal may be filtered to only select signals at that frequency (e.g. 10kHz). This filters out any noise due to IR in the ambient variation andin particular fluctuations in the IR in the ambient light.

The touch system described herein may be calibrated in order to cancelout any unwanted reflections inherent in the design which may arisefrom, for example, reflections from within the LCD panel. Suchcalibration may also be used to overcome any variations betweendifferent units and within a single unit die to tolerances in themanufacturing process. Calibration may also be used to cancel outartifacts due to ambient lighting conditions which may vary with time.Initial calibration (e.g. to overcome manufacturing artifacts) may beperformed by detecting the level of light without any items touching thedisplay or being in proximity to the display. This background level maythen be subtracted from any subsequent measurements. Dynamic calibrationmay be carried out instead of or in addition to the initial calibrationby regularly capturing background levels even when the touch panel isoperating, using certain techniques to differentiate between changes insensed background levels and changes due to interaction with the touchpanel. For example, when no change in the received IR levels aredetected these levels may be used for subtraction from detected signalsinstead of the initial calibration results. In a further example,detected levels may be analyzed and any fixed touch events which do notchange over a defined period of time (e.g. in the order of minutes) maybe discounted. Such calibration may be applied across the entire touchpanel, or may be applied to sub-areas of the panel. In another example,when no change in received IR levels are detected, re-calibration may beinitiated.

FIG. 5 shows a schematic diagram of a further touch panel 500 whichcomprises an LCD panel 501 with IR sources 502 and IR detectors 503located behind the LCD panel (i.e. on the opposite side to the touchsurface 504). In order to reduce the stray IR detected by the detectors,which may result in detection of spurious touch events, a mask layer 505may be placed behind the LCD panel which is made of a material which isopaque to IR and which has holes which are aligned with the sources anddetectors. In some examples, a second layer 506 may be included betweenthe mask layer 505 and the LCD panel 501. This second layer 506 may bemade of a material which is transparent to IR and which reflects visiblelight. This means that viewers of the touch panel system cannot see themask pattern irrespective of their viewing angle.

Where a large touch panel system comprises multiple touch panels (e.g.to create a large touch panel wall) the sources in the panels may beswitched on sequentially (e.g. alternating panels at any one time) andthe detection in the panels synchronised with the switching of thepanels. This reduces the overall power consumption and reducesinterference caused by stray reflections within and between the panels.

In order to reduce the power consumption of the touch panel system, anintelligent algorithm may be used to only illuminate IR sources around atouch point, as shown in FIGS. 6 and 7. FIG. 6 shows a schematic diagramof an example touch panel 600 which comprises an array of IR sensors 601and an array of IR sources 602. In other examples, one or more IRsources may be used with a light guide (as described above). A scan ofthe entire panel (block 701) may be used to detect touch events (block702), e.g. a touch event in the area indicated by dotted circle 603 andthen sources around the detected events (e.g. those within dotted circle604) may be illuminated (block 703). The entire panel scan (block 701)may be repeated periodically (e.g. at 1 Hz, 10 Hz etc) to detect touchevents. The interval between entire panel scans may be fixed or may bevariable dependent on battery life (e.g. larger intervals for lowerbattery life). In another example, shadow mode may be used for the scanof the entire panel (in block 701).

In a variation on the method of FIG. 6, the area around the detectedtouch event may be scanned at a higher frame rate (e.g. 50 Hz) than theentire panel. In this example, the overall power consumption may not bereduced.

In the above description, the use of a single IR wavelength (or a narrowrange of wavelengths) is described. However, in order to distinguishbetween multiple objects placed on the touch panel system, each objectmay comprise a wavelength selective tag or label, which may then be readusing different wavelengths of IR (e.g. 850 nm, 980 nm or more closelyspaced wavelengths), as shown in the example flow diagram of FIG. 8. Thetouch surface is illuminated with IR of wavelength λ_(n) (block 801) andthe reflected signal detected and analyzed to identity any objects(block 802). The process is then repeated for the next wavelength(blocks 803, 801, 802) etc. In some examples, a combination of detectionof the shape and the wavelength of the tag may be used to distinguishbetween objects (in block 802).

The wavelength selective tag may be in the form of a coating on part ofor the entire surface of the object which is in contact with the touchpanel system. The tag may, for example, comprise a holographic film, aBragg grating, a wavelength-selective thin film or any otherwavelength-selective reflector.

In order to use such wavelength selective reflectors to distinguishbetween objects, the touch panel may comprise IR sources of differentwavelengths (e.g. a first array emitting IR wavelength λ₁ and a secondarray emitting IR wavelength λ₂). When IR sources of a first wavelength,λ₁, are turned on (in block 801), bright reflections will be detected(in block 802) from those objects having a tag which reflects thatwavelength and when IR sources of a second wavelength, λ₂, are turned on(block 803, then block 801), bright reflections will be detected (inblock 802) from those objects having a tag which reflects the secondwavelength. As described earlier, the touch panel may in some examplesnot comprise an array of sources but instead one or more IR sources ofeach wavelength may be used in combination with a light guide. Inanother example, the touch panel may comprise one or more tunable IRsources (e.g. a tunable LED or a tunable laser) and the objects may bedetected and distinguished by scanning the wavelength of the tunablesource.

In another example, color sensing may be used to further differentiatedifferent barcodes. In this example, IR light may be used to detect thepresence of an object, and then white illumination and color detectorsused to determine an object's identity (or to assist in thisidentification).

The objects may, for example, be gaming pieces, physical user interface(UI) devices, such as dials, sliders etc, identity tags for users (e.g.to log in a user may place his/her tag on the touch panel, where theuser is identified by the wavelength of the wavelength-selective tag, orthe tag in combination with other distinguishable features) or any otherobject.

Whilst in the example above, the tags on objects may be selective usingwavelength, in other examples other optical properties may be used toprovide wavelength selective tags, such as the angle of illumination(e.g. by powering different sources, moving sources etc), intensity orpolarization of the illuminant. The tag may comprise a holographic film,a thin light pipe or any suitable selective reflector.

Whilst use of reflective mode alone is suitable for many applications,there may be situations where the use of both shadow and reflectivemodes provides an improved touch detection system (e.g. one which isless sensitive to varying lighting conditions). For example when thelevel of ambient IR falling on sensors not occluded by a fingertip issimilar to (or greater than) the level of reflected light falling onsensors that are underneath the fingertip, reflective mode will not bevery effective. Such a touch panel may comprise the same elements asthose described above (e.g. that shown in FIG. 2) or alternatively thetouch panel may comprise additional sensors for use in shadow mode.

There are many ways in which shadow mode and reflective mode may both beused by a touch panel system:

-   -   use of shadow mode for portions of the touch panel where the        ambient light level exceeds a threshold    -   use of shadow mode to provide a low power consumption mode    -   use of both shadow mode and reflective mode to detect a        particular object or to provide additional information about the        object (e.g. depth, thickness etc)    -   use of both shadow mode and reflective mode data to distinguish        between touch and no touch events        Each of these are described in more detail below with reference        to FIGS. 2, 6 and 9-12.

As described above, there may be situations where the level of ambientIR falling on the sensors is high which reduces the effectiveness ofreflective mode for detection of touch events. Therefore, as shown inFIG. 9, the touch panel system, which may comprise touch panel 600, asshown in FIG. 6, may detect the level of ambient IR (block 901) and ifthe detected level does not exceed a defined threshold (‘No’ in block902), reflective mode is used (block 903) for the detection of touchevents. However, if the detected level does exceed that threshold (‘Yes’in block 902), shadow mode may be used instead (block 904). Thisdecision may be taken on the basis of the whole panel (i.e. if the levelof ambient IR at any point on the panel exceeds the threshold, thenshadow mode is used instead of reflective mode) or alternatively, thedecision may relate to portions of the panel (e.g. shadow mode is usedfor those portions of the display where the ambient IR exceeds thethreshold). The portions may be of fixed size (e.g. the panel may besegmented into 6 portions and if the ambient IR at any point in thatpanel exceeds the threshold, then shadow mode is used for that portion)or of variable size (e.g. shadow mode is only used in the particulararea where the ambient IR exceeds the threshold). As described above,the threshold (used in block 902) may be set based on a known maximumpossible level of reflected IR.

Reflective mode is a more power hungry mode of operation than shadowmode, because of the requirement to power the IR sources and thereforein some examples, shadow mode may be used to provide a low power mode ofoperation of the touch panel, as shown in FIG. 10. This low power modeof operation may be used when the battery level falls below a certainlevel, when user enabled, during periods of inactivity or at any othertime (referred to herein as ‘low power mode criteria’, assessed in block1001). In an example, the touch panel may use shadow mode (block 904)during a period of inactivity (i.e. no touch events detected in block901, resulting in a ‘Yes’ in block 1001), however, when a potentialtouch event is detected in shadow mode (resulting in a ‘No’ in block1001), the IR sources may be illuminated for all or a part of the touchpanel such that reflective mode can be used for detection of the touchevent (block 903). After a further period of inactivity (a subsequent‘Yes’ in block 1001), the touch panel system may revert back to shadowmode (block 904). This low power mode may be enabled on the entire touchpanel or on portions of the panel and the criteria may be assessed (inblock 1001) on the basis of the entire panel or portions of the panel.

In a further example, aspects of these two techniques may be combined asshown in the example flow diagram of FIG. 11 such that the low powershadow mode is only able to be enabled (e.g. based on a period ofinactivity or other criteria, as described above, determined in block1001) where the ambient light exceeds a defined threshold (as determinedin block 1101). This ensures that the touch panel system does not enterthe low power mode in a situation where a touch event cannot be detectedusing shadow mode and therefore the touch panel system would not receivea ‘wake-up’ signal as described above which causes it to change intoreflective mode. The threshold used to determine whether a low powermode may be used (in block 1101) will be different to the threshold usedto determine that reflective mode may be less suitable (in block 902),e.g. it will be set at a lower level of ambient IR. If the panel enterslow power mode, the level of ambient light and the criteria for the lowpower mode may be monitored periodically or constantly, as indicated bythe dotted arrow (from block 904 to block 1101).

The decisions (in blocks 902, 1001, 1101) may be made by a controlelement within the touch panel system. The control element may beimplemented using logic in hardware, or the control element may comprisea processor and memory (e.g. as shown in FIG. 17 and described below).

As shown in FIG. 2, the position of sensors detecting the reflectedlight in reflective mode may be offset from the actual position of theobject on or adjacent to the touch panel. When both shadow andreflective modes are used, the sensors detecting the shadow caused by anobject on or close to the touch panel may be different from thosedetecting the reflected light. Analysis of the different detectionpatterns in each mode, obtained by modulating the IR sources anddetecting the shadow in the periods when the IR source is off, may beused to obtain information on the distance between the object and thetouch panel surface (referred to herein as ‘depth detection’) or todetermine between a touch or no touch situation. In a simple example, anobject which is not in contract with the screen will cast a largershadow; however the amount of reflected light will be less than if itwas in contact with the screen.

Use of shadow mode, instead of or in addition to reflective mode todetect depth (or to make touch/no touch decision) enables a moreaccurate detection because the curve on distance detection forreflective mode (i.e. power detected vs. distance) is not monotonic,whilst the corresponding curve for shadow mode is monotonic. Detectionof touch/no touch may be implemented using an adaptive threshold, whichmay be adapted based on the detected ambient light level or based on thedetection of an approaching object using shadow mode. In other examples,the detection may use two thresholds (one for reflective mode and onefor shadow mode).

Dependent on the ambient light, multiple shadows may be cast by anobject. In some circumstances this may provide additional 3D informationabout an object, e.g. as shown in FIG. 12, with a first shape 1201detected in reflective mode and a second shape 1202 detected on shadowmode. By processing the two images (i.e. the sensor data from the arrayof sensors), it is possible to determine that the object is, in thisexample, shaped like a pyramid. Whilst in other examples, it may not bepossible to determine the exact shape of the object, analysis of the twodetected images (one from reflective mode and one from shadow modeoperation) may provide information on the approximate shape or thicknessof the object (e.g. is it a planar object like a piece of paper or doesit have substantial thickness like the gaming pieces shown in FIG. 1).

In addition to, or instead of, using a combination of shadow andreflective modes, the IR sources within the touch panel may be switchedon and off (or modulated at higher speed) in groups such that the angleof illumination of an object changes dependent upon the group of sourceswhich are switched on (e.g. odd columns/rows followed by evencolumns/rows). In some examples, the illumination pattern may be variedbased on the detected shape (e.g. to illuminate additional or differentsources around the periphery of the detected shape). Analysis of thedetected signals for each group of sources may provide some 3Dinformation about the object (e.g. is it thin like a sheet of paper ordoes it have appreciable thickness), may improve the accuracy of thedetected shape and may also enable the cancellation of any specularreflections e.g. due to the user wearing a ring. This may also reducethe overall power consumption of the touch panel system, which may beparticularly useful where the system is battery operated and reduceinterference caused by stray reflections within the touch panel.

In another example, instead of providing different sets of IR sources,the position of the light source in the touch panel may be movable. Bymoving the source, the angle of illumination is again changed, thereforeenabling detection of 3D information. The same effect may be achieved bymoving a light guide which guides light from an IR source.

In another embodiment, the touch panel may control the ambient lighting.This control may, for example, use a Bluetooth, X10, IrDA (as describedbelow) or other wireless link. In such an embodiment the touch panel maycontrol ambient light sources (which emit IR and may also emit visiblelight) so as to provide an optimised environment for use of shadow (orreflective) mode and/or to change the lighting angle to obtain depth/3Dinformation, as described above. A computer vision system may be used toanalyze the combined signals from the detectors within the system andcontrol the ambient lighting based on the levels detected.

Instead of, or in addition to, controlling the ambient lighting, thecombined detected signals may be analyzed and the IR sources controlledbased on the detected signals. This allows the touch panel to compensatefor variations in IR ambient light across the touch panel which mightotherwise degrade the sensing ability.

In a further example, the touch panel may further comprise an array ofdetectors which are sensitive to visible light. In a similar manner tothat described above, the combined detected signals from these visiblelight detectors may be analysed and used to control the brightness ofparts of the image displayed on the touch panel. This may be achieved,for example, by changing the brightness of the back light or some of theLEDS in a LCD display. This enables the touch panel to compensate forvariations in ambient visible light (e.g. due to sunlight or shadows ona portion of the display). The visible detectors (and sources) may alsobe used to assist in the identification of objects in proximity to thetouch surfaces, as described above.

In addition to detection of touch events, the IR sources and/or sensorsmay be arranged to enable data communications between the screen and anearby object. The communications may be unidirectional (in eitherdirection) or bi-directional. The nearby object may be close to or incontact with the touch surface, or in other examples, the nearby objectmay be at a short distance from the touch screen (e.g. of the order ofmeters or tens of meters rather than kilometers).

In a first example, as shown on FIG. 13, the touch panel 1300, which maycomprise an array of infra-red detectors 1301 (e.g. IR sensitive TFTs orIR-sensitive photodiodes), may receive an IR signal from a nearby device1302 including an IR transmitter 1303. The operation, as shown in FIG.14 involves the detection of the signal at one or more of the detectors(block 1401) and changing the display dependent upon the detected signal(block 1402). The display may be changed (in block 1402) in manydifferent ways, for example:

-   -   Display of a pointer icon on the touch panel dependent on the        position of the detector receiving the signal. This provides a        pointer system for use with a touch panel. This system may be        used in many applications including presenting, gaming etc.    -   Changing the user interface (UI) according to the detected        pointing parameters (e.g. location, modulation scheme etc, as        described in more detail below). This enables the movement of        the device 1302 (e.g. when the user gestures or points) to be        used to control the images/data displayed, navigation through        various windows of a UI etc.    -   Controlling the application running on the display system        according to the pointing parameters.

The signal transmitted by the nearby device 1302 may use any suitableprotocol, such as the standard TV remote control protocol or IrDA. Theshape of the beam projected by the nearby device may be controlled (e.g.a circle, square or cross-shaped) and may be fixed or variable. Thechange to the display (e.g. the pointed icon displayed) may be dependentupon the shape detected and/or any other parameter detected in relationto the IR signal (e.g. the modulation scheme used, as described in moredetail below). The shape detected may also be used to determine thelocation of the person holding the device with respect to the touchpanel and where a cross-hair is used, the rotation of the device may bedetermined. This may enable the image displayed to change based on theuser's location or an aspect of the game to be controlled based on thedetected pointing parameters (e.g. shape, modulation scheme etc).

Aspects of the detected signal may, in some examples, be used tocalibrate the response to signals received. For example, the intensityof the detected signal may be used to determine the approximate distancebetween the device 1302 and the touch panel 1300 and the response todetected signals (in block 1402) may be changed based on thisdetermination. In an example, where the touch panel system detectsgestures, the size of the expected gesture may be normalised based onthe determined distance between the device and the touch panel.

In order that the display can distinguish multiple pointing eventssubstantially simultaneously, different devices may use different beamshapes, different wavelengths or different modulation (e.g. amplitudemodulation) schemes. In an example, the signal may be modulatedaccording to an identifier associated with the device (e.g. a BluetoothMAC address) such that the information may be used to identify thedevice and for subsequent communication (e.g. by Bluetooth in thisexample).

In a further example, different pointing events may be distinguishedusing spatial multiplexing. In this example, the detected signal frommultiple detectors may be analyzed (e.g. using a computer vision system)to determine whether two beams are being received (e.g. because thereare two spatially separated groups of detectors which are detecting thesignal or the shape detected is a partially overlapping combination oftwo known beam shapes). In another example, different nearby devices1302 may be allocated different time slots for transmission of a pulsedIR signal (i.e. time division multiplexing) or different wavelengths maybe used.

Such a device 1302 may provide a user interface device for the touchpanel. The touch panel may be arranged to interpret the detected shapesas user inputs (e.g. rotation of cross-hairs, gestures etc) and therebycontrol an application running on the display (e.g. use of gestures tomove items between different displays). This may be combined with datacommunications between the touch panel and the device (e.g. if a userpresses a button on the device) and this is described in detail below.Such a device, may for example, provide a games controller and thedetection of multiple pointing events, as described above, may providemeans for multiple players to interact with the game via the touch panelsubstantially simultaneously. In an example, the nearby devices maycomprise games controllers and the detection of multiple pointing eventsmay enable a multiplayer shooting game to be played on the touch panelsystem.

In addition to having an IR transmitter 1303, the device 1302 may alsocomprise a visible transmitter (not shown in FIG. 13) such as a visiblelaser or LED. In such an example, the visible transmitter may be usedfor pointing and the IR transmitter may be used for data communicationsto control the application which is running. The application may be apresentation application (such as Microsoft PowerPoint (trade mark), agame or any other application.

In a second example of communications with a touch panel using IR, thesignal received (e.g. from nearby device 1302) may comprise data(encoded in a modulated signal), rather than being a pointer signal. Asshown in FIG. 15, the modulated IR signal which comprises data may bereceived at one or more of the sensors 1301 in the touch panel (block1501) and then stored (block 1502). In order that data may be receivedfrom more than one device substantially simultaneously, spatial,frequency or time division multiplexing may be used in a similar mannerto detection of multiple pointing events, as described above. Asdescribed above, any suitable protocol may be used, such as IrDA.

In addition to, or instead of, receiving data from a nearby device, thetouch panel may transmit data to one or more nearby devices, as shown inthe schematic diagram of FIG. 16. The touch panel 1600 comprises, inaddition to an array of IR sensitive detectors 1301, one or more IRsources 1601 which may be used to illuminate nearby objects for use inreflective mode (as described above). One or more of the IR sources 1601may be used to transmit data (indicated by beam 1602) to a nearbyelectronic device 1603 equipped with an IR receiver 1604 or a dedicatedIR source may be provided for data transmission. The data may bebroadcast such that all electronic devices which are within range canreceive the data, or alternatively the data may be transmitted usingdifferent modulation schemes, or multiplexing techniques (e.g. spatial,frequency or time) in order to transmit different data to differentdevices.

In some examples, a DC-balanced encoding scheme is used for datatransmission between the touch panel and one or more nearby devices.This data transmission is modulated at a rate faster than that requiredby the touch panel to detect a specified type of touch event, such as afingertip touch. In this way, the touch panel is able to carry out datatransmitting substantially simultaneously with touch event detection.

In some examples, the touch panel system is arranged to detect theoutline of a nearby electronic device (such as 1302 of FIG. 13) eitherin reflective mode or shadow mode. This enables the touch panel systemto detect the presence of the nearby electronic device and to “expect”possible data communication with that nearby device. For example, thetouch panel system may be arranged to switch at least some of thesensors within the detected outline into data communications mode.

Whist the nearby devices in FIGS. 13 and 16 are depicted as a pointingdevice 1302 and a mobile telephone 1603 this is by way of example onlyand the touch panel may communicate with any nearby device comprising anIR transmitter and/or receiver. The devices may be located close to orin contact with the touch panel (e.g. intelligent game pieces) or at adistance from the touch panel (e.g. laptop or desktop computer, PDA,games console, games controller, light controller etc).

The data transferred between a nearby device and the touch panel may beof any kind, including data for display on the touch panel, such asimages captured on a digital camera (which may, for example, beintegrated within a mobile telephone or PDA). In another example, thedata transferred may be an identifier (e.g. the ID of a pointing deviceor the identifier for a particular data set which should be displayed onthe touch panel). In an example, an identifier for a particular data setmay be transmitted from the touch panel to a nearby device and then agesture may be used to transfer that data set to another touch paneldisplay system.

In order to reduce the power consumption of the touch panel, the touchpanel may only scan a subset of the sensors 1301 and upon detection of asignal (e.g. in block 1401 of FIG. 14), the panel may scan all thesensors 1301 in order to determine the full parameters of the signal(e.g. to determine the aspects of any gesture in detail).

FIG. 17 illustrates various components of an exemplary computing-baseddevice 1700 which may be implemented as any form of a computing and/orelectronic device, and in which embodiments of the methods and apparatusdescribed above may be implemented.

Computing-based device 1700 comprises a touch panel 1701, for example asdescribed above and shown in any of FIGS. 2, 3, 5, 6, 13 and 16, and oneor more processors 1702. The one or more processors may bemicroprocessors, controllers or any other suitable type of processorsfor processing computing executable instructions to control theoperation of the device in order to detect multiple touch/pointingevents and/or to transmit or receive data to/from a nearby device. Thecomputer executable instructions may be provided using anycomputer-readable media, such as memory 1703. The memory is of anysuitable type such as random access memory (RAM), a disk storage deviceof any type such as a magnetic or optical storage device, a hard diskdrive, or a CD, DVD or other disc drive. Flash memory, EPROM or EEPROMmay also be used.

Platform software comprising an operating system 1704 or any othersuitable platform software may be provided, and stored in memory 1703,to enable application software 1705 to be executed on the device. Theapplication software may include a computer vision system application1706.

The computing-based device may also comprise one or more inputs whichare of any suitable type for receiving media content, Internet Protocol(IP) input, user instructions from a user input device etc, acommunication interface and one or more outputs such as an audio output.

Although the present examples are described and illustrated herein asbeing implemented in an IR based system, the system described isprovided as an example and not a limitation. As those skilled in the artwill appreciate, the present examples are suitable for application in avariety of different systems which may use different wavelengths ofelectromagnetic radiation (e.g. visible light). In addition, instead ofusing the arrangement of IR sources described above, the touch panel mayuse FTIR (frustrated total internal reflection) where the IR sourceemits a beam parallel to the touch surface and the IR sensors detect adrop in intensity.

The term ‘computer’ is used herein to refer to any device withprocessing capability such that it can execute instructions. Thoseskilled in the art will realize that such processing capabilities areincorporated into many different devices and therefore the term‘computer’ includes PCs, servers, mobile telephones, personal digitalassistants and many other devices.

The methods described herein may be performed by software in machinereadable form on a storage medium. The software can be suitable forexecution on a parallel processor or a serial processor such that themethod steps may be carried out in any suitable order, orsimultaneously.

This acknowledges that software can be a valuable, separately tradablecommodity. It is intended to encompass software, which runs on orcontrols “dumb” or standard hardware, to carry out the desiredfunctions. It is also intended to encompass software which “describes”or defines the configuration of hardware, such as HDL (hardwaredescription language) software, as is used for designing silicon chips,or for configuring universal programmable chips, to carry out desiredfunctions.

Those skilled in the art will realize that storage devices utilized tostore program instructions can be distributed across a network. Forexample, a remote computer may store an example of the process describedas software. A local or terminal computer may access the remote computerand download a part or all of the software to run the program.Alternatively, the local computer may download pieces of the software asneeded, or execute some software instructions at the local terminal andsome at the remote computer (or computer network). Those skilled in theart will also realize that by utilizing conventional techniques known tothose skilled in the art that all, or a portion of the softwareinstructions may be carried out by a dedicated circuit, such as a DSP,programmable logic array, or the like.

Any range or device value given herein may be extended or alteredwithout losing the effect sought, as will be apparent to the skilledperson.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Itwill further be understood that reference to ‘an’ item refer to one ormore of those items.

The steps of the methods described herein may be carried out in anysuitable order, or simultaneously where appropriate. Additionally,individual blocks may be deleted from any of the methods withoutdeparting from the spirit and scope of the subject matter describedherein. Aspects of any of the examples described above may be combinedwith aspects of any of the other examples described to form furtherexamples without losing the effect sought.

It will be understood that the above description of a preferredembodiment is given by way of example only and that variousmodifications may be made by those skilled in the art. The abovespecification, examples and data provide a complete description of thestructure and use of exemplary embodiments of the invention. Althoughvarious embodiments of the invention have been described above with acertain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this invention.

1. A method of operating a touch panel system for detecting one or moreobjects in proximity with a touchable surface of a touch panel, themethod comprising: scanning at least a portion of the touch panel tomeasure a level of ambient infrared radiation using at least oneinfrared sensor; switching to a shadow mode of operation if a level ofambient infrared radiation exceeds a first threshold; switching to areflective mode of operation if the level of ambient infrared radiationdoes not exceed both the first threshold and a second threshold;determining that a battery level is below a predetermined limit whilethe level of ambient infrared radiation exceeds the second threshold andnot the first threshold; switching to the shadow mode of operation afterthe battery level drops below the predetermined limit; and switching tothe reflective mode of operation after the battery level rises above thepredetermined limit.
 2. A method according to claim 1, wherein scanningat least a portion of the touch panel further comprises: scanningdifferent portions of the touch panel dependent upon time and uponsignals from the infrared sensors.
 3. A method according to claim 1,wherein the first threshold is higher than the second threshold.
 4. Amethod according to claim 1, wherein the touch panel system furthercomprises a plurality of infrared sources configured to illuminate theobjects with infrared radiation through the touchable surface, themethod further comprising, in reflective mode of operation: scanning thetouch panel; and on detection of a touch event at an infrared sensor,illuminating those infrared sources in proximity to said infraredsensor.
 5. A method according to claim 1, further comprising, inreflective mode of operation: illuminating the touchable surface withinfrared radiation of a first wavelength; detecting infrared radiationreflected from an object at said first wavelength; and repeating theilluminating and detecting steps at a second wavelength.
 6. A methodaccording to claim 1, further comprising, periodically recalibrating thetouch panel system based on the scanning at least the portion of thetouch panel.
 7. A touch panel system for detecting one or more objectsin proximity with a touchable surface of the touch panel system, thetouch panel system comprising: a touch panel having integrated thereininfrared sensors distributed throughout the touch panel parallel to thetouchable surface; at least one infrared source configured to illuminateobjects through the touchable surface; and a control element arrangedto: scan at least a portion of the touch panel to measure a level ofambient infrared radiation; switch to a shadow mode of operation if alevel of ambient infrared radiation exceeds a first threshold; switch toa reflective mode of operation if the level of ambient infraredradiation does not exceed both the first threshold and a secondthreshold; determine that a battery level is below a predetermined limitwhile the level of ambient infrared radiation exceeds the secondthreshold and not the first threshold; switch to the shadow mode ofoperation after the battery level drops below the predetermined limit;and switch to the reflective mode of operation after the battery levelrises above the predetermined limit.
 8. A touch panel system accordingto claim 7, wherein the control element comprises: a processor; and amemory arranged to store executable instructions arranged to cause theprocessor to monitor signals from the infrared sensors and switchbetween the reflective mode of operation and the shadow mode ofoperation for at least a portion of the touch panel based on themonitored signals.
 9. A touch panel system according to claim 8, furthercomprising an array of infrared sources, wherein the memory is furtherarranged to stored executable instructions arranged to cause theprocessor, in the reflective mode of operation, to: scan the touchpanel; and on detection of a touch event at an infrared sensor; toilluminate those infrared sources in proximity to said infrared sensor.10. A touch panel system according to claim 7, wherein the objectcomprises a wavelength selective tag or label which can be read usingdifferent wavelengths of IR that enables the object to be distinguishedfrom another object.